1. Technical Background
The present invention relates generally to medical devices, and more particularly to balloon catheter tip designs, and methods of making such catheter tips.
2. Discussion
Balloon catheters are used in a variety of therapeutic applications, including many vascular treatments such as angioplasty, and delivery of medical devices such as stents. Angioplasty can be used to treat vascular disease, in which blood vessels may be partially or totally blocked or narrowed by a lesion or stenosis. In many instances of vascular disease, a local area of a blood vessel may become narrowed. This narrowing is called a lesion or stenosis, and may take to form of hard plaque, cholesterol, fats, or viscous thrombus. Such a stenosis may cause heart attack or stroke, which are significant health problems affecting millions of people each year.
During angioplasty, an expansive force may be applied to the lumen of the stenosis, which may be a vessel constriction or narrowing due to plaque buildup or thrombus, etc. This outward pressing of a narrowing at the desired site in a body passage is intended to partially or completely reopen or dilate that body passageway or lumen, increasing its inner diameter or cross-sectional area. The objective of this procedure is to increase the inner diameter or cross-sectional area of the vessel passage or lumen through which blood flows, to encourage greater blood flow through the newly expanded vessel.
After or during angioplasty, a mesh scaffold called a stent may be deployed in the vessel passage. The stent will generally be allowed to remain permanently, tending to hold open the vessel.
The present invention relates to methods of joining polymer tubes and to resulting assemblies of joined polymer tubes. A prior method of joining two polymer tubes is to select two tubes having the same or similar inner and outer dimensions, place their ends together and heat them to form a simple heat-seal or “butt fuse”. The tubes may be cylindrical or not, including for example tubes having a cross-section that is square, rectangular, triangular, or any other regular or irregular polygon. Also, the tubes may have the same inner and outer dimensions, or the inner and/or outer dimensions, or the inner and/or outer dimensions may be slightly different, as long as overlapping or abutting surfaces are defined.
A butt seal can be made easily and quickly. However, a butt seal may present a sharp transition in material characteristics, such as lubricity or flexibility. Also, a butt seal may itself be less flexible than is desirable, or may be less strong of a joint than is desirable.
In contrast, the present invention joins polymer tubes such that the joint itself is flexible, and is stronger than other methods. Using the principles of the present invention, at least two polymer tubes are placed in contact. These tubes will be referred to as the “joinder tubes.” They may contact each other in an abutting or overlapping arrangement, or a combination of both. A shrink tube is placed around the polymer tubes to be joined (the joinder tubes). The shrink tube tends to radially shrink when heated, and may have a high lubricity and a higher melting temperature than the joinder tubes. A mandrel is inserted within the joinder tubes. The mandrel may be a metal wire or other suitable material thin enough to pass through the lumens of the joinder tubes.
To join the joinder tubes, the shrink tube is heated to cause the joinder tubes to melt slightly, or to a temperature greater than the glass transition temperatures or melting temperatures of the joinder tubes, and the mandrel is moved while the shrink tube imparts inward radial pressure on the joinder tubes. The movement of the mandrel may be along a longitudinal axis in one direction or the opposite direction, or it may be moved back and forth, and/or it may be rotated.
The resulting seal is strong and flexible, with a transition zone of blended material properties, rather than an abrupt transition.
As an example, the present invention will be described in relation to coronary, peripheral, and neurovascular angioplasty and/or stenting. However, it should be understood that the present invention relates to any catheter having polymer tubes joined with a method using the features of the present invention, and is not limited to catheters for a particular therapeutic treatment. Another example of the present invention is any two polymer tubes, for example the main shaft of a catheter, that are joined using a shrink tube, heat, and a moving mandrel.
Some balloon catheters have a relatively long and flexible tubular shaft defining one or more passages or lumens. The shaft extends between a hub at a proximal end to a distal end, and a balloon is located near the catheter distal end. The catheter shaft defines an inflation lumen for conducting inflation fluid from an inflation port defined by the proximal hub to the balloon interior, so a physician can selectively inflate or deflate the balloon.
The shaft may also define a guidewire lumen extending from a distal guidewire port at the distal end of the catheter to a proximal guidewire port located at a position proximal from the balloon. The proximal guidewire port may be defined by the hub, referred to as an “over-the-wire” arrangement, or may be positioned at some intermediate point on the shaft between the hub and balloon, referred to as a “rapid exchange” arrangement. Structurally, the guidewire lumen may be defined by a tubular inner body extending from a distal end of the catheter proximally through the entire length of the balloon catheter. Whatever structural element defines the guidewire lumen, the inner diameter or cross-sectional area of the guidewire lumen is preferably large enough to accommodate the size of the desired guidewire. Likewise, the inner diameter of the guidewire lumen in the region of the balloon may be constant, to facilitate easy movement of the guidewire within the guidewire lumen.
One possible shaft design is a coaxial arrangement of tubular inner and outer bodies. A balloon defines an interior volume and has a proximal leg and a distal leg, with the distal balloon leg being affixed to a distal end of the inner body, and the proximal balloon leg being affixed to a distal end of the outer body.
During a common treatment method for using such a balloon catheter, a physician advances the catheter into the body of the patient, by directing the catheter distal end percutaneously through an incision and along a body passage, until the balloon is located within the desired site. The term “desired site” refers to the location in the patient's body currently selected for treatment by a physician.
As the balloon catheter is advanced along the desired vascular path, the performance of the catheter design may be evaluated by analyzing various characteristics, including flexibility, lubricity, pushability, trackability, crossability, low profile and others. Flexibility may relate to bending stiffness of a medical device (balloon catheter and/or stent, for example) in a particular region or over its entire length, or may relate to the material hardness of the components. Lubricity may refer to reducing friction by using low-friction materials or coatings. Pushability may relate to the column strength of a device or system along a selected path. Trackability may refer to a capability of a device to successfully follow a desired path, for example without prolapse. Crossability may be clarified by understanding that physicians prefer to reach the desired site with the balloon catheter while encountering little or no friction or resistance. Profile may refer to a maximum lateral dimension of the balloon catheter, at any point along its length.
As an example of prior balloon catheters, U.S. Pat. No. 6,402,720 entitled “Balloon Catheter With Elongated Flexible Tip”, issued to Miller et al. on Jun. 11, 2002 shows a balloon catheter having a hub, a catheter shaft having an outer and inner tube, a balloon and a flexible tip.
These and various other objects, advantages and features of the invention will become apparent from the following description and claims, when considered in conjunction with the appended drawings.